Pulse producing apparatus



Dec. 19, 1950 L. A. MEACHAM 2,534,872

- PULSE PRODUCING APPARATUS original Filed June 22, 1945 4 Sheets-Sheet 2 RANGE INDICATOR Li A A v. Q 8

49 WENTOR I LAMEACHAM BY ATTORNEY Dec; 19, 1950 L. A. MEACHAM 2,534,872

PULSE PRODUCING APPARATUS Original Filed June 22, 1943 4 Sheets-Sheet 3 f76.3| m 49 R3! .22 96 48 9/ 23% 1 I ll 1 Hi l a k F/Gd C49 A TTOR/VE Dec. 19, 1950 L. A. MEACHAM 2,534,872

PULSE PRODUCING APPARATUS Original Filed June 22, 1945 4 Sheets-Sheet 4 Acf/v: PER/0D GUIESCENT PER/0D 1:; U filllllllll-llll 1 llllllllllllll IOYO POTENTIAL IN VOLTS V GNDO- I Z0 TIME 0 m/vavroe L. A ME A CHA M ATTORNEY Patented Dec. 19, 1950 PULSE PRODUCING APPARATUS Larned A. Meacham, Summit, N. J., assignor to Bell Telephone Laboratories, Incorporated, New York, N. Y., a corporation of New York (briginal application June 22, 1943, Serial No.

491,791. Divided and this application December 14, 1946, Serial No. 716,294

8 Claims.

This invention relates to pulse producing apparatus and particularly to such apparatus which is of use in producing an indication of the range of a distant object.

In accordance with an embodiment of the invention herein shown and described for the purpose of illustration, there are provided means for generating, during an interval which occurs between the time of radiation of an impulse of a series of impulses from a transmitter and the time of reception by a receiving apparatus of an echo of the radiated impulse from a distant object, a series of alternate positive and negative impulses of brief duration recurring at predetermined equal intervals and means for causing the selection of one of the series of impulses by superposing it upon a pedestal impulse which is started under control of, and coincidentally with, the impulse immediately preceding the selected impulse. Means are provided for varying and measuring the delay interval between the time of radiation of an impulse and the time of occurrence of the selected one of the series of impulses, the indicating means being preferably calibrated in units of distance so that, when the selected impulse is delayed by the required amount to bring it into coincidence with the received echo of the radiated impulse, there is produced an indication of the distance from the impulse radiator and receiver to the object from which the echo is received.

To facilitate the manual adjustment of the apparatus for bringing the selected impulse into coincidence with a received echo, a visual indicating device such as a cathode ray tube is preferably provided. The echo impulse, together with the selected impulse or a range impulse controlled by the selected impulse, are impressed upon the vertical deflecting plates, for example, of the cathode ray tube. The horizontal deflection of the cathode ray beam produced in the cathode ray tube is controlled by a deflecting wave or precision sweep which is initiated simultaneously with the starting of the pedestal under control of the impulse which initiates the pedestal. The position of the range pulse is fixed near the center of the screen of the cathode ray tube; and the position of the echo pulse, when the object is stationary and the delay adjustment remains unchanged is also accurately fixed so that jittering or to and fro movement of the visual indications is avoided 'ivhen, as is the practice, impulses are radiated and echoes are received in rapid succession. When the object moves, or the delay adjustment is changed, the echo appears to progress smoothly across the screen.

The brief pulses of a high frequency radio wave which are radiated toward an object are produced at intervals under control of starting pulses which may be generated under control of an alternating electromotive force of relatively low frequency, say 400 cycles per second, one starting pulse being produced at about the same point in each cycle of the 400 cycle wave. These starting pulses are also used for controlling the so-called range unit constructed in accordance with the present invention. The starting pulses are impressed upon a circuit, called a start-stop circuit herein, which generates a square topped voltage Wave having a negative portion the duration of which is equal to or preferably greater than the maximum delay occurring between the time of production of a starting impulse and the reception of an echo of the radiated pulse from an object the distance of which is to be measured. Durin the interval that the square topped impulse produced by the start-stop circuit is positive the start-stop circuit i returned to its stable waiting condition ready to be started again by a succeeding start impulse. This interval is preferably short with respect to the length of the negative portion of the square topped wave so that range impulses may be transmitted in rapid succession. The start-stop circuit employs two electric discharge devices (the electrodes of which may be within a single envelope), the anode of one device being connected through a condenser to the control grid of the second device as in a multi-vibrator circuit. It has been found that by connecting the anode of the second device to the control grid of the first device directly by a conductive connection instead of connecting the anode to the grid through a condenser as in the usual multivibrator circuit, the recovery time of the circuit is considerably shortened.

A timing wave generator is started due to the abrupt decrease in potential at the start of the negative portion of the square topped wave from the start-stop circuit. The generator frequency is accurately maintained at a constant value so that the period of one cycle will be equal at all times to the predetermined interval required for a range impulse to travel from a radiator to an object a definite distance away and for its echo to return. Quenching of the oscillatory wave produced by the generator is started clue to the abrupt rise in potential occurrin at the beginning of the positive portion of the square topped wave produced by the start-stop circuit and the generator is designed so that the quenching is completed within the relatively short period of the positive portion of the square topped wave. The timing wave generator is coupled to a phase shifter by means of a phase inverter circuit which provides an accurately balanced low impedance input to the phase shifter and is designed to present an extremely high impedance to the antiresonant circuit of the timing wave generator to which it is coupled. In order to minimize the time requirement for the phase shifter to reach stead state response to each group of timing oscillations, the phase shifting circuit is designed so that it presents a substantially pure resistance load to the output of the phase inverter circuit to which it is coupled. The phase shifting condenser of the phase shifter is an improvement over the condenser disclosed in my United States Patent No. 2,004,613, granted June 11, 1935. It is designed to simplify its manufacture, to provide complete shielding, to avoid use of moving contacts and to obtain satisfactory capacitive balances through inherent mechanical symmetry.

The timing Wave is supplied from the output of the phase shifter to an amplifier the output of which is connected to a pulse generator which produces a series of alternate positive and negative sharp pulses, these pulses being accurately spaced by the predetermined interval mentioned. The amplifier is a high gain linear amplifier with negative feedback to present an extremely high impedance to the phase shifter and to avoid drawing an appreciable resistive component of current through the small capacity of the phase shift condenser which would cause distortion of the timing wave. The amplified timing Wave is impressed upon an electric discharge device circuit which functions as a cathode follower during positive half cycles of the amplified timing wave, and which device is cut off during the negative half cycles to effectively clip the timing wave along its center line, the negative half of the timing wave impressed upon the input circuit of this center clipper being discarded. The clipped timing wave appears with reversed polarity in the plate circuit of this device. An electric discharge device coupled to the center clipper circuit is alternately cut off and turned on again by the square topped portion of the inverted center-clipped wave to produce a series of alternate positive and negative timing impulses. The sharpness of response of the timing pulse generator is improved by providing a delay in the negative feedback of the center clipper to momentarily impart high gain to the center clipper tube at the beginning of each positive half cycle of the timing wave.

The square topped wave from the startstop circuit is also applied to an RC delay circuit to cause discharge of a capacitance through a resistance which may be varied to change the time constant of the discharge circuit, thereby causing an exponentially rising potential to be applied to the control grid of an electrical discharge device. The potential difference to which the capacitance is charged is proportional to the resistance of the variable resistor. alternate positive and negative timing impulses are impressed upon the cathode of the electric discharge device which is maintained, during the intervals between impulses, at a potential which is directly proportional to the initial potential The series of difference to which the capacitance is charged. When the control grid potential of the discharge device has thus been increased sufiiciently with respect to the cathode potential, a negative pulse from the timing pulse generator will decrease the cathode potential sufficiently to cause the discharge device to pass space current. A rapid decrease in potential at the anode of the device thus takes place. The time of production of this negative step or impulse is determined by the setting of the variable resistor which controls the time constant of the condenser discharge circuit and also by the phase shift of the series of impulses produced by shifting the phase of the wave from the timing wave generator.

The negative impulse produced at the output of the RC delay circuit controls a circuit for gen-- erating a square topped impulse or pedestal and a sweep wave for controlling the horizontal deflection of a cathode ray beam. The pedestal which is initiated coincidentally with a negative pulse from the timing pulse generator is added to the timing pulse with the result that the positive pulse which immediately follows that'negative pulse is superposed upon the pedestal. The superposed impulse may therefore be selected and used to perform a desired function. When a cathode ray indicator is used, the selected timing pulse may be impressed on the vertical deflecting means to produce an indication of the range of an object from which an echo pulse is received, the echo pulse also being impressed upon the vertical deflecting means. Instead of applying the se-. lected timing pulse directly to the cathode ray tube for indicating the range, the timing pulse may be used to generate a step or notch pulse with which the echo pulse may be aligned on the cathode ray tube screen for producing a range indication.

The shaft of the phase shifter condenser which causes the phase of the timing wave to be varied is geared to the shaft of the variable resistor of the RC delay circuit through a step-down gear ratio such that the interval between a starting pulse and the following selected timing pulse may be varied continuously over a range starting from a value near zero to a value corresponding to maximum range. A revolution counter associated with the shaft of the phaseshifting condenser is calibrated to indicate the distance to the object from which an echo is received when the selected timing pulse is delayed by such an amount that it occurs simultaneously with the received echo.

If desired, apparatus may be employed for automatically varying the capacity of the condenser of the phase shifter and the variable resistor of the RC delay circuit when the received echo falls out of synchronism with the selected timing pulse to maintain the echo and the selected timing pulse in synch-ronism. Such an apparatus is disclosed in an application of B. M. 0liver Serial No. 491,829, filed June 22, 1943.

The invention will now be described with reference to the accompanying draw-ing in which:

Fig. 1 is a block diagram of a ranging system in accordance with the present invention;

Fig. 1A consists of curves to which reference will be made in describing the invention;

Figs. 2 and 3, when Fig. 3 is placed below Fig. 2, are a schematic view of a range indicator in accordance with the invention;

Fig. 4 is a schematic view of a modification of a portion of the apparatus shown in Fig. 3;

Fig. 5 is a view in elevation of a phase shifting condenser which is used in the range indicator of Figs. 1, 2 and 3;

Fig. 6 is a sectional view taken along the line 6-6 of Fig. 5; and

Fig. 7 is a diagram to which reference will be made in explaining the operation of the invention.

Referring now particularly to Figs. 1 and 1A? there is disclosed a range indicating system in which recurring brief pulses of electromagnetic wave energy produced by a radio transmitter 10 and radiated from an antenna H are directed toward an object the distance of which is to be determined and in which the reflected wave impulses or echoes are received by an antenna l2 and detected by a radio receiver 13. An oscillator M produces a sinusoidal wave having a period somewhat longer than the time required for a radio wave to travel twice the maximum distance to be measured. Starting pulse generator It: produces sharp impulses as indicated at a in Fig. 1A at regular intervals, one for each cycle of the sine wave from oscillator [4. It is not essential to the operation of the system, however, that these impulses be produced at regular intervals. The starting impulses which are preferably of very brief duration, say microsecond, key the radio transmitter it to cause corresponding pulses of high frequency radio wave energy to be radiated from the antenna i l.

The starting pulses a are impressed upon the start-stop circuit E6 of a range unit (which comprises apparatus within the area defined by the dash-dot line It) for generating a square topped voltage wave 1). The initial negative portion ll of wave 1) is started at the time of a start impulse a, that is at time to, and has a duration slightly longer than the time required for a radiated wave pulse to travel twice the maximum distance to be measured. The startstop circuit then recovers its stable waiting condition during a period which is short with respect to its active period during which the negative impulse El is produced. The positive portion it of the wave 1) is produced during this recovery period.

If the frequency of oscillator M is varied below a certain maximum value, the duration of the negative portion ll remains fixed, while that of the positive portion l8 varies, above a certain minimum duration for recovery.

The voltage wave 1) produced by the start-stop circuit [6 is impressed upon a timing wave generator 23 which generates a constant frequency oscillatory wave 0 the phase of which may be shifted by a phase shifter 2| continuously through a plurality of cycles by turning the handle I23. The phase shifted wave is indicated at d. The period of this oscillatory wave or a phase shift of the wave through a single cycle corresponds to the time interval required for a radiated wave to travel through a certain distance and for its echo to return through that distance. The distance represented by the period of a single cycle of the oscillatory wave is the velocity of propagation of the radiated impulse divided by twice the frequency of the oscillatory wave. The timing wave generator is started by the starting transient at the beginning of the negative portion ll of the wave 2) from the start-stop circuit [6 and is quenched due to the stop transient which occurs at the beginning of the positive portion 18 of wave b. The timing wave d from the phase shifter is impressed upon a pulse generator 22 which produces alternate positive and negative timing. pulses as indicated at e of Fig. 1A, a pulse being produced at the beginning of each half cycle of the timing wave.

It is desired to produce a pedestal impulse upon which a certain one of the timing impulses may be superposed so that that timing impulse may be selected and used. Means are required for shifting the pedestal with respect to time in synchronism with the shifting of the timing impulses so that one impulse of each series of impulses may be superposed upon the pedestal. There is provided an RC delay circuit 23 having a condenser which is discharged, at a rate determined by the setting of a variable resistor,

during the'period defined by the "portion H of the wave b from the start-stop circuit 16. The shaft 34 of the variable resistor of the RC delay circuit is connected through gears 24 to the condenser shaft 29 of the phase shifter if so that the change in time constant of the condenser discharge circuit is proportional to the phase shift of the timing wave (1 and of the timing impulses e. The timing impulses e are also impressed upon the RC delay circuit for accurately fixing the time of generation of the pedestal impulse and the sweep wave.

A voltage impulse produced at the output of the RC delay circuit as indicated by the curve E34 of Fig. 7, is impressed upon the pedestal and sweep Wave generator 25. There is produced by this circuit a pedestal pulse 9 and a sweep wave 11. each of which accordingly is started at the time of the negative pulse which immediately precedes the positive pulse which is to be selected for use in producing a range indication. The pedestal pulse 9 and the pulses e from the pulse generator 22 are combined to cause a certain positive pulse 26 of the timing pulses e to be superposed upon the pedestal 21 as shown at i so that the pulse 26 may be used to produce a range indication. The selected timing pulse 26 may be used directly for range indication or, as shown in Figs. 1 and 1A a step impulse a may be produced under control of the selected pulse 26 by the step generator 28. The sweep wave is amplified by an amplifier 35.

The step 7' and the echo impulse from the radio receiver 13 are impressed upon the vertical deflecting plates 3| of a cathode ray tube 30. The sweep wave h is impressed upon the horizontal deflecting plates 32 of the cathode ray tube. By manually rotating the shaft 29 of the phase shifter condenser to which the shaft 34 of the variable resistor of the R. C. delay circuit is geared, an echo pulse may be caused to travel along the luminescent screen of the cathode ray tube until it is brought into alignment with the step 7'. The distance to the object from which the echo is received may then be read from a revolution counter or range indicator I50 attached to the shaft 29, each revolution of the shaft producing an indication equal to a certain fixed distance. As pointed out above, the received echo and the selected timing pulse may also be used, if desired, to control automatic apparatus which causes the shaft 29 to rotate when the distance to an object from which the echo is being received changes so that the changin range of the object can be read from the indicator I58 without requiring manua1 adjustment of the apparatus.

The range indicating apparatus is shown in greater detail in Figs. 2 and 3 when Fig; 3 is placed below Fig. 2. Current from a 400 cycle 7 source 14 is supplied to the primary windings of transformers B and BI of the starting pulse generator l5. employing a. gaseous discharge de vice 62 having an anode, a cathode, and a control grid. Voltage from the secondary winding of transformer BI is supplied to the control electrode-cathode circuit of tube 62 through a suitable phase shifting circuit comprising a shunt condenser 03, internal impedances of transformer 6i, and a protective resistor 04 such that the critical grid voltage required to cause cur rent conduction through the discharge tube is reached when the anode is at or near the positive peak of the voltage wave applied to the anode circuit from' the secondary winding of transformer 00. A 500 micromicrofarad condenser is charged through a, series circuit connected to the secondary winding of transformer 60 which comprises 1,000 ohm'resistor 00 and 1,800 ohm resistor 5?. When the critical grid voltage of the tube 62 is reached, condenser 0'5 discharges through a circuit comprising inductance element 63 of 50 microhenries, anodecathode path of the tube 02, .024 microfarad condenser 00 having 30,000 ohm resistor 70 connected in parallel therewith and thence through 1,800 ohm resistor 01. The condenser 65 is thus quickly discharged (in about microsecond) sufficiently to cause the voltage at the anode of tube 02 to be reduced and the discharge current through the tube to be interrupted. The radio transmitter l0 comprises a multicavity magnetron which may be of the type disclosed in Patent 2,063,342 to Samuel, December 8, 1935, for example. The magnetron comprises an anode H which forms an external sheath or enclosure, a cathode '72, a loop '43 and a magnet 74. The anode'H and one end of loop 13 are grounded, the other end of the loop being connected through a coaxial conductor cable 75 to antenna Ii. During the short interval of each cycle of the alternating current source l4 when the gaseous discharge tube 02 is conducting, there is thus impressed between the anode i1 and cathode 72 a high direct current voltage to cause the production of high power, ultra-high frequency oscillations which are picked up by the loop 73 and transmitted through the coaxial conductor line 55 to the directive transmitting antenna i I. a .003 micromicrofarad condenser H connected in series between the anode of tube 02 and ground, are also charged by current from source i4 through a circuit comprising transformer 00,, resistor 60 and inductance element 68. The discharge of the condensers through the anodecathode path of tube 02 through the brief interval when the tube is conducting causes a nega tive starting impulse (a of Fig. 1A) to be impressed upon the coaxial conductor line 59'which transmits the impulse to the start-stop circuit I6.

The start-stop circuit it employs an electric discharge device comprising two triodes, the one having a cathode 4!, a control electrode 42 and an anode 43 and the other having a cathode 44, a control electrode and an anode 46. Negative starting impulses from the coaxial conducter line 59 are applied through a 10 micromicrcfarad condenser C'i across 0.5 megohm resistorRI- which is connected between the control electrode 42 and ground. The cathode 4! is connected to ground. The anode 43 is directly cond-uctively connected to the control electrode 45 and the anode 46 is connected to the control grid 42 through a condenser C8 the capacity of which A 3 micrornicrofarad condenser and 8 is micromicrofarads when the maximum range to be measured is 20,000 yards. The cathode 44 is connected to ground through 20,000 ohm resistor R0 shunted by .0002 microfarad condenser C9. Anode potential is applied to the anode 43 from the positive terminal of 300 volt battery 5! through series resistors R4 (1,000 ohms) and R3 (0.1 megohm) the negative battery terminal being grounded. Positive voltage is supplied to the anode 46 from source 5i through series resistors R4, R8 (40,000 ohms) and R! (60,000 ohms). The positive terminal of battery 5| is also connected through series resistors R4 and R5 (60,000 ohms), to the cathode 44. A 20 microficrofarad condenser CH is connected in shunt with respect to the resistor R1. A 0.1 microfarad condenser CH} is connected across the series current path comprising resistors R0, R1, R0 and the anode-cathode path from anode 46 to cathode 44.

During the quiescent period of the start-stop circuit !6, the triode 4!, 42, 43 is fully conducting with the grid 42 held at the potential of cathode 4! by resistor RI, and the anode 43 is reduced to a low voltage by the passage of anode current through R3. The grid 45 is held at a potential which is actually negative with respect to cathode 44 which is maintained at about volts by the voltage divider R5 and R6. As triode 44, 45, 46 is thus biased below cut-oi? the anode 46 rests at about +300 voits. The circuit remains stably in this condition until a starting impulse is applied.

The negative starting impulse from the starting impulse generator I5 applied to the grid 42 causes the grid to become negative with respect to its cathode and the current flowing through the discharge path from anode 43 to cathode 4| is decreased. As a result the potential of anode 4 5 and of grid 45 is sharply increased to produce a negative impulse at the anode 46 due to current flowing through the discharge path from anode 46 to cathode 44, this negative impulse being impressed upon grid 42 by way of condenser C8 to reinforce the starting impulse and thus trigger the leading edge of the start-stop wave 17. Thereafter the potential of grid 42 rises exponentially toward its asymptote at cathode potential with a time constant of approximately (RI) (C8). The active period of the range unit is determined by the time required for the potential of grid 42 to rise to its cut-off potential. When the grid 42 reaches its cut-01f potential the stop transient occurs, the triode 4!, 42, 43 becoming conducting and the grid 45 being carried down to its quiescent low potential to make the triode 44, 45, 46 nonconducting. The potential of anode 46 thus rises sharply until triode 4!, 42, 43 begins to draw grid current. Thereafter the potential at anode 46 rises somewhat more gradually because condenser C8 is charged exponentially by current passing through R8, B1, C8 and the grid-cathode path of triode 44, 42, 43. As the grid-cathode impedance is low, the recovery time constant is essentially (C0) (RH-R8) which is short compared to the time constant (RI) (08), so that the circuit may recover its stable waiting condition in a time considerably shorter than its active period. The negative portion H, of the start-stop wave 1) which may be about six times (R!) (GB), for example, is produced during the active period while triode 41, 42, 43 is cut ofi and the shorter positive portion l8 of wave 0 is produced during the quiescent period when triode 4 I 42, 43 is conducting. The shortening of the quiescent time period is believed to be due to the omission of the usual coupling condenser between the anode 43 and the grid 45 so that these elements are directly conductively connected. Condenser C9 is used to lead 52 to the timing wave generator 20 comprising an oscillatory circuit in the anode current path of an electric discharge device 53, and the timing wave from the generator 20 is impressed upon a phase inverter circuit of the phase shifter 2|, which circuit comprises an electric discharge device 54. The phase inverter circuit is connected to a circuit comprising a variable condenser C21 for shifting the phase of the wave from timing wave generator 20. Each ofthe electric discharge devices 53 and 54 comprises a cathode, a control grid, a screen grid, a suppressor grid, and an anode. The lead 52 from the start-stop circuit is connected through a 0.1 microfarad condenser Cl2 and 10,000 ohm resistor RID to the control electrode of discharge device 53 which is connected through 1 megohm grid leak resistor R9 to the grounded cathode. Positive potential is supplied from the 300 volt source 5| to the anode of tube 53 through 500 ohm resistor RIZ, through the antiresonant circuit comprising inductance element LI and .005 microfarad condenser Cl5 in parallel and through 6,400 ohm resistor RH and .003 microfarad condenser CM to the tube anode, the antiresonant circuit being tuned to cause the generation of a 65.57 kilocycle wave during the interval when tube 53 is rendered non-conducting due to the negative portion I! of the start-stop wave b, Fig. 1A, impressed thereon. A relatively large capacity condenser Cl5 is used in order that variations of stray capacity may not affect the frequency appreciably. The oscillatory wave is quenched by the low impedance of tube 53, after the positive portion I8 of the start-stop wave raises the grid of tube 53 above cut-oil. Positive potential from the 300 volt source 5| is applied to the screen grid of tube 53 through a circuit comprising resistor R12, the anti-resonant circuit Ll, CIS and 20,000 ohm resistor RI3. The inductance LI and the condenser C of the antiresonant circuit are enclosed within a chamber the temperature of which is maintained constant by a suitable temperature controlling apparatus (not shown) so that the frequency of oscillation is maintained constant. The frequency of 65.57 kilocycles was chosen because the period of the wave of this frequency is equal to the time required for a radio wave to travel 5,000 yards, that is, from a transmitting antenna to an object 2,500 yards distant and back to a receiving antenna in proximity to the transmitting antenna. In some cases it will be desirable to choose a timing wave having a difierent period.

The common terminal of the antiresonant circuit and the parallel circuit comprising element CM and RH is connected through .001 microfarad condenser C|8 to the control grid of the phase inverter tube 54. A 100 micromicrofarad variable condenser C2 connected between the control grid of tube 54 and ground is provided to permit a small manufacturing adjustment of frequency of the oscillatory circuit. The 16 microfarad filter condenser CNS is connected from the negative terminal of resistor Ri2 to ground.

The phase inverter circuit is used to provide an accurately balanced low-impedance input to the phase shifter. It also employs cathode feedback to present an extremely high input impedance to the antiresonant circuit, thus minimizing damping and stray capacitance effects. The anode current path of electric discharge tube 54 may be traced from the positive 300 volt terminal through 1,000 ohm resistor R2i, 1,000 ohm resistor R20, 6,000 ohm resistor R19, the anodecathode path of tube 54, R ohm resistor R84, 6,000 ohm resistor RIB and 1,000 ohm resistor Rl! to ground. RI! and R20 are equal resistances across which the balanced output voltages appear. R18 is used to increase the amount of cathode feedback for the purpose of obtaining high input impedance and RIS balances the resistance of R is in the anode circuit. The anode current through R80 produces a voltage drop which is applied to the control electrode for biasing it through a filter formed by .1 megohm resistor RM shunted by a .001 rnicrofarad condenser CIG and through ,5 megohm resistor Rl5. This arrangement further magnifies the resistance component of the input circuit. Positive voltage from the 300 volt source is supplied to the screen grid through R2! and 0.25 megohm resistor R22. The screen grid is connected to the cathode through .006 microfarad condenser C2! so that the alternating screen grid current flows through the tube Without affecting the external anode and cathode circuits. One terminal of resistor R22 is connected through condenser C2l to the cathode and the other terminal of R22 is connected through .5 microfarad condenser C24 to ground. With respect to the alternating timing voltage, therefore, resistor R22 is effectively in shunt with the resistors connected in the circuit between cathode and ground. The resistance of R22 is therefore balanced by the .25 megohm resistor RIG connected between the anode and the common terminal of resistors R20 and RZI. Capacitive unbalance of the anode and cathode to ground is corrected by a variable micromicrofarad condenser Cl, shunted by 50 micrornicrofarad condenser Cll, connected between ground and, through .001 microfarad protecting condenser C20 to the anode of tube 56.

The balanced output of the phase inverter is connected through .1 microfarad condensers C22 and C23 to a phase splitting circuit comprising two parallel paths the one path comprising 750 micromicrofarad condenser C26, a 75 micromicrofarad variable condenser Cd being in shunt with C26, connected in series with 3,000 ohm resistor R21, and. the other path comprising 3,000 ohm resistor R26 connected in series with 750 micrornicrofarad condenser C25, !5 micromicro-- sectors 8!, 82, 83, 3d and a dielectric rotor 81 having a dielectric constant materially different from that of air. The rotor may also be made of metal grounded or insulated from ground, but the dielectric rotor is preferable. The dielectric rotor is mounted on a metallic shaft 29 the bearings for which are provided by the outer casing 85, the latter also providing shielding. Thestator members 8|, 82, 83, 8 and 80 are supported by insulating members 39 from the casing 85. The four-phase voltages are supplied to th stator sectors 8|, 82, 82 and 84 which are equal in area and shape and are accurately parallel to the ring stator 86. The casing 85 is connected to a metallic shield 90 around a first amplifier stage of the pulse generator to which the output of the phase shifter is connected, the shield being grounded.

It will be seen that the potentials impressed upon opposed stator sectors of the phase-shifting condenser are 180 degrees out of phase while the potentials at any two adjacent sectors are 90 degrees out of phase. All four potentials are of equal amplitude.

If the resistance R20 or that of R21 is equal to R and the capacitance of C26 and C4 in parallel or that of C25 and C3 in parallel is equal to C, then each of the two parallel paths of the phase splitting circuit satisfies the equation A. 21rfC' where X is the capacitive reactance and f is the frequency. The load impedance Z1 presented by these elements to the phase inverter circuit, neglecting any small effect of C21 is In order to minimize the time required for the phase shifter to reach steady state response to each timing wave produced during the period defined by the negative portion [1 of a start-stop wave, it is desirable to have this impedance a pure resistance. This is realized by connecting the path comprising inductive element L2 having an inductance of 3.64 millihenries in series with 1,500 ohm resistor R24 in shunt with the path comprising C21 and R25 and with the path comprising R26 and C25, this added impedance due to L2 and R24 being equal to the conjugate of Z1, that is Under this condition the load impedances Z1 equals for all frequencies up to a high harmonic of the timing wave, which therefore appears undistorted on stator sectors 8! and 83. The phase shifted waves on stator sectors 82 and 84 approach their steady state condition by way of an exponential starting transient the time constant T of which is equal to RC. Since which corresponds to one radian of the timing wave. It is desirable that this transient be short so that the timing wave may be sufficiently accurate for the measurement of short ranges. The condenser Ci may be set permanently in manufacture so that the over-all calibration of the range unit in yards is precisely correct for two diametrically opposed positions of the phase shifter condenser C21 and the range calibration may be made correct for two angular positions at right angles to the first-mentioned positions by manufacturing adjustment of the trimmer condensers C3, C4. The accuracy at intermediate positions of the condenser C21 is dependent upon the amplitude balance. of the. voltages on the. four stator sectors and. upon the similarity of the four sectionsv of the condenser C21.

The ring stator 86. of the phase shifter is connected by lead 49 to the input of a two-stage amplifier comprising electric discharge tubes 9! and 92, and the output of the amplifier is connected to a timing pulse generator circuit comprising electric discharge tubes 93. andv 94. The lead 49 is connected to the control grid of tube. 9 I. Anode potential is supplied to the tube from the 300 volt source 5! through 1,000 ohm resistor R31 and 100,000 ohm resistor R1, the cathode of the tube 9! being connected through 500 ohm resistor R30 to ground. Control grid biasing potential is provided due to the anode current flowing through R30, which bias is supplied to the grid. through .1 megohm resistor R28 and 2 megohm resistor R29 in series. A .01 microfarad condenser C28 in a path connecting the cathode of tube 9| to the common terminal of resistors R28 and R29 by-passes alternating components of the voltage across R30. Screen grid voltage is supplied to tube 9! from the 300 volt source through resistor R31 and through .5 megohm resistor R32. A .01 microfarad condenser C30 is connected between the screen grid and the cathode. The anode of tube 9| is connected through .01 microfarad condenser C29 to the control grid of amplifier tube 92. Anode voltage is supplied to tube 92 from the 300 volt source through resistor R31 and 20,000 ohm resistor R36 and screen grid voltage is supplied from the 300 volt source through resistor R31 and 60,000 ohm resistor R38, the screen grid being connected through .1 micromicrofarad condenser C32 to the cathode. Resistor R35 of ohms is connected between the cathode of tube 92 and ground to produce a grid biasing voltage due to anode current flowing therein, which bias is supplied to the grid through the .1 megohm resistor R34. Condenser C3! of .1 microfarad suppresses alternating components of the voltage across R35. Ne ative feedback is provided by connecting [anode of tube 92 through .3 megohm resistor R33 to the cathode of tube 9!. The use of a large resistorfor R29 together with the negative feedback makes the input impedance of the amplifier extremely high so that no appreciable resistive component of current is drawn through the very small capacity of the phase shifting condenser C21. Displacement of the center-line of the timing wave (particularly during the first gew cycles of each train) with the resultant errors in range indications are thus avoided. Condenser C34 of .5 microfarad is connected between ground and one terminal of resistor R31 to suppress voltage variations of the 300 volt source.

The amplified timing wave voltage at the anode of tube 92 is impre sed through .01 microfarad condenser C33 upon the control grid of a center clipper tube 93. The control grid is connected through .1 megohm resistor R39 to ground and the tube cathode is connected through 10,000 ohm resistor R40 shunted by .0001 microfarad condenser C36 to ground. Anode voltage is supplied to tube 93 from the 300 volt source through 1,000 ohm resistor R45 and 20,000 ohm resistor RM and screen grid voltage is supplied from thevoltage divider formed by re istor R45, .1 megohm resistor R42 and .1 megohm resistor R43, the screen grid being: by-passed to the cathode 13 through .1 microfarad condenser C31. The tube 93 acts as a cathode follower for the positive half cycles of the timing wave impressed upon its grid and it is cut off during the negative half cycles. During the positive half cycle on the grid when the grid potential first increases and then decreases, the anode potential decreases and then increases. While the tube is out off the anode potential is constant. The anode of tube 93 is connected through .001 microfarad condenser C35 to the grid of electric discharge tube 94, the cathode of which is grounded. Anode voltage is supplied to tube 94 through resistor R45, through 1,000 ohm resistor R4! and through 5,000 ohm resistor R46. Screen grid voltage is supplied to the tube through resistor R45 and .1 megohm resistor R48, the screen grid being connected through .1 microfarad condenser C39 to ground. Condenser C65 (0.1 microfarad) is connected from the negative terminal of resistor R95 to ground. During the quiescent period when no wave is generated by the timing wave generator, the control grid of tube 94 is at a slightly positive potential, the 399 volt source connected through resistor R45 and .1 megohm resistor R44 to the control grid causing a small grid current to flow. During the active period when the timing wave is generated, the change in anode potential of tube 93 causes the grid potential of tube 94 to be sharply increased at the beginning of one-half cycle of the timing wave and to be sharply decreased at the beginning of the following half cycle so that tube 94 is made conducting and non-conducting alternately. As a result, a train of square waves with sharp corners is produced at the anode of tube 94, which is connected to the step impulse generator 29, and at the common terminal of resistors R95 and R41, which is connected to the RC delay circuit. Difierentiation of the square waves produces alternate negative and positive sharp impulses e.

The RC delay circuit comprises four electric discharge tubes 95, 99, 9'! and 98. The squaretopped Wave from the start-stop circuit is im pressed upon the control grid of tube 95 through .1 microfarad condenser 039, the control grid being connected to the cathode through 1 megohm grid leak resistor R5!. There is provided a current path from the 300 volt source through 8,000 ohm resistor R50, through constant voltage discharge device or cold cathode tube I and through 4,000 ohm resistor R99 to ground. The resistance of the constant voltage device changes as the current through it varies to maintain the voltage across the tube constant. A 16 microfarad condenser C50 is connected from the common terminal of resistor R50 and cold cathode tube I00 to ground. The cathode of tube 95 is connected through resistor R49, having .1 microfarad condenser C92 connected in parallel therewith to ground, to maintain the cathode potential at substantially 50 volts positive With respect to ground. During the quiescent periods when the start-stop Wave is positive, anode current flows through tube 95 from the 300 volt source, through 8,000 ohm resistor R50, through 200,000 ohm rheostat R52, through the anodecathode path of tube 95 and through resistor R49 to ground.

A 1,500 micromicrofarad condenser C4! connected in parallel with 150 microinicrofarad condenser 009 and rheostat R52 is thus charged to a voltage equal to the voltage drop across the rheostat which, of course, willdepend upon the rheostat setting. A trimmer condenser C5 of 100 micromicrofarads is connected in a circuit from the anode of tube through .005 microfarad protecting condenser C45 to ground to provide an adjustment of the time constant of the circuit (R52) (041). Screen grid voltage is supplied from the 300 volt source through 30,000 ohm resistor R59. The anode of tube 95 is connected to the control grid of the cathode follower tube 96 having its cathode connected through 20,000 ohm resistorR5=i to ground. Anode potential is supplied to tube 96 from the 300 volt source through 1,000 ohm resistor R55. The cathode of tube 96 is connected to the control grid of tube 98 which, in turn, is connected through .1 megohm resistor R58 to the mid-tap of transformer winding 99' which supplies heating current to the cathode heater of tube 95. Anode potential is supplied to tube 98 from the 300 volt source through resistor R55 and l megohm resistor R60. The common terminal of R59 and the cold cathode tube I99, which is maintained at substantially 200 volts positive with respect to ground, is connected through 35,000 ohm resistor R5! and 60,000 ohm resistor R56 to the cathode of tube 96. The resistors R56 and R5? are voltage-dividing resistors, the common terminal of which is connected to the cathode of tube 91. The 200 volt terminal of resistor R5! is connected through .002 microfarad condenser C99 to the anode of diode tube 9?, which anode is connected through 1,000 ohm resistor R59 to the cathode of tube 99. The initial voltage to which the condenser 04! is charged when tube 95 is conducting, and therefore the initial potential at the anode of tube 95, at the grid and cathode of tube 96 and at the grid of tube 98, is determined by the setting of rheostat R52. Assume that the initial potential at the cathode of tube 95 and at the grid of tube 98 is E0 volts below 200 volts. When tube 95 becomes non-conducting due to the negative portion or the start-stop wave impressed upon its control grid, the condenser G i l and its trimmers will discharge through R52 and the potential at the cathode of tube 96 and at the grid of tube 98 will rise exponentially from its initial voltage toward the 200 volt asymptote. When tube 98 is not conducting, condenser C46 is charged to a voltage equal to the potential across resistor R5? through the anode-cathode path of tube 91', this voltage being 51 (approx.)

below the 200 volt asymptote. Timing impulses e from the timing pulse generator 22 are impressed upon the cathode of tube 98 through condenser C97 of 100 micromicrofarads. Condenser 091 and 1,000 ohm resistor R59 provide the necessary difi'erentiating action When the potential at the grid of .tube 99 has increased sufiiciently with respect to its cathode potential due to the discharge of condenser 09!, a negative timing impulse will lower the cathode potential of tube 98 suficiently to cause the tube to conduct and the cathode potential will then also rise exponentially due to the change in the charge on condenser C50. The charge on condenser (345 is changed due to current from the 300 volt source flowing through R55, R69, the anode-cathode path of tube 98, R59, condenser C46,.R5'I, R50 and R50 to ground. Thus during an: interval which varies with the setting of rheostat R52, the condenser C II discharges to such a'potential that the tube is caused to conduct at the instant that a certain negative impulse from the timing impulse generator is impressed upon its cathode. A sudden decrease in voltage is therefore produced at the anode of tube 98. The operation of the RC delay circuit will be further clarified by reference to the curves of Fig. '7 which will be discussed later. i

The pedestal and sweep wave generator 25 comprise electric discharge devices IOI, I02 and I03. The device IOI comprises two triodes, the

one having a cathode I00, a control grid I and an anode I00 and the other having a cathode I01,

a control grid I08 and an anode I09. The sharp negative pulse produced at the anode of tube 03 of the RC delay circuit 23 is impressed through 100 micromicrofarad condensor C08 upon the control grid I05 to interrupt the flow of anode current which is supplied from the 300 volt source through 1,000 ohm resistor R01, .1 megohm resistor R03 to the anode I00, the cathode I00 being connected through 20,000 ohm resistor R52 shunted by .1 microfarad condenser C00 to ground. The grid is connected through 5 megohm grid leak resistor R6! to the cathode. The anode I00 is connected through 100 micromicrofarad condenser C50 and 50,000 ohm resistor R05 to the control grid I08. Thus when the anode current is interrupted in triode 04, I05, I00 a positive impulse is impressed upon the grid I08 to cause anode current to flow from the 300 volt source through resistors R01 and R00 (1 megohm), the anode-cathode path and R02 to ground. The triode I0l, I08, I00 must remain conducting until the pedestal impulse and sweep wave are completed and therefore the resistor R05 is used in the path between the anode I06 and the grid I08 to block any pulses which may be passedthrough tube 90 and the triode I00, I05, I06 by way of the plate-to-grid capacitances. Electric discharge tube I02 is a triode having a control grid, a cathode and an anode. Discharge tube I03 has a cathode H0 and anodes III and H2, forming two diodes. It also has an anode I I3 and a control grid I M which, with the common cathode I I0, form a triode. Anode N39 is connected through 100 micromicrofarad condenser CES to the grid of tube I02 and through 100 micromicrofarad condenser C55 to the grid II4 of tube I03. When triode I01, I08, I09 is made to conduct its anode voltage drops from plus 300 volts to a low value. The grid of tube I02 and the grid II4 of tube I03, which are normally slightly above cathode potential, are thus carried negative about 150 volts. After the grids of tubes I02 and I03 are thus displaced negatively, the grid potentials rise exponentially toward plus 300 volts due to the charging of condensers C53 and C55 through resistors R08 (1 megohm) and R73 (.25 megohm) respectively, from the voltage drop across R00. The triode I02 and the triode portion of tube I03 are thus made non-conducting due to the negative impulse from the RC delay circuit and, after a short interval, these triodes again become conducting.

Anode current is supplied to tube I02 from the 300 volt source through resistor R6? and .2 megohm resistor R00, the cathode being connected through 50,000'ohm resistor R10 shunted by .0015 microfarad condenser 052 to ground. Anode current is applied to the triode of tube I03 from the 300 volt source through R61 and .1 megohm resistor R14, the cathode I I0 being grounded. -A horizontal sweep wave for the deflection of a cathode ray beam is produced due to the discharging 'of condenser C52 through resistor R70 when tube I02 is cut off and due to its subsequent charging caused by the voltage drop across R10 when anode current flows therethrough. The sweep voltage across condenser C02 is impressed through 1 megohm resistor RH having .01 microfarad condenser C50 connected in shunt therewith, upon the lead 2I4 going to a sweep amplifier II5. During the quiescent perod when the start-stop wave is positive, the lead 2 I is stably located at ground potential as required for the sweep amplifier due to the lead 2H! being connected to the anode III of one of the diodes of tube I00. Similarly, when the triode portion of tube I03 is cut 011, its platepotemtial rises momentarily to produce a squaretopped impulse or pedestal g which is impressed through 2 megohm resistor Hi2 shunted by .001 microfarad condenser C00 upon lead H5 going to the step generator 28. By connecting the lead 2I5 to the anode H2 of a diode of tube I03, the peak of the pedestal is located at approximately ground potential, the major part of the wave being held correspondingly negative.

The pedestal impulse is supplied through lead 25-5 and 10,000 ohm resistor R15 to the control grid of electric ischarge device H0 of the step generator 20. The timing impulses from the timing pulse enerator 22 are also impressed upon the grid of tube H0 by way of lead II? and. 20 micromicrofarad condenser C52. In this case, difierentiation of the square wave from the anode of tube =0 is performed by C51 and. R1 5, resulting in the sharp pulses e. Anode current is supplied to tube H0 from 300 volt source 55 through 1,000 ohm resistor Ri8 and 1 megohm res stor R'il to the anode. Current is also supplied from the 300 volt source through the volt age dividing resistors R170 of .1 megohm and R70 of 15,000 ohms, which is shunted by .01 microfarad condenser C03, the positive terminal of resistor R70 being connected to the cathode of tube M0 to maintain it at a positive voltage with respect to ground. Screen grid voltage is supplied from the 300 volt source through resistors R10 and R (10,000 ohms), the screen grid being connected through condenser C50 of .0005 microfarad to ground. The negative terminal of resistor BT10 is connected through .1 microfarad condenser C03 to ground. The anode of tube I I0 is connected, through 5 micromicrofarad condenser C00 and in shunt therewith a circuit comprising 2 megohin resistor RM and -.001 microfarad condenser C0! in series, to a short length of coaxial conductor cable H3 going to a vertical deflecting plate I22 of the cathode ray tube I 25. The other vertical deflecting plate and one of horizontal deflecting plates I2I are grounded; A circuit comprising resistor R82 of 200 ohms in series with micromicrofarad condenser C02 and in shunt with said series circuit a .1 megohm resistor R03 is connected between the coaxial conductor cable H0 and. ground. When the tube H0 passes anode current due to the pedestal pulse impressed upon its control grid a sharp negative impulse is produced at the anode of tube H0 and impressed upon the coaxial conductor cable H0, condenser C62 being charged very rapidly to about 10 volts negative with respect to ground. Continued flow of current is limited by means of small bypass condenser C00 in the screen grid supply circuit and the small coupling condenser C00.

1'? Resistor R83 provides a discharge path for the discharge of condenser C82 to form the exponentially rising portion of the step wave 7'. Resistor RBI and condenser CBI in series are connected in shunt to 080 to improve the wave form of the step.

In addition to the vertical and horizontal defleetin plates, the cathode ray device I25 comprises a cathode H9, anodes I 29, and a phosphorescent screen 523. At the time that the pedestal pulse 9 is started the sweep wave h is also started and the latter is impressed upon the horizontal deflecting plates i2i from the output of the sweep amplifier H5. The step wave from the step generator and the echo pulse from the output of the radio receiver I3 are impressed upon the vertical deflecting plates 522 of the cathode ray tube. The step impulse and the echo impulse are thus visually reproduced upon" the screen 23 and, due to the echo pulses being received and the step or range impulses being produced in succession at a rate within the period of persistence of vision, the echo indication is stationary upon the screen when the object from which the echoes are received is stationary, and the range impulse or step is always stationary upon the screen. By rotating the shafts of the phase shifter and RC delay circuit by means of a handle I25, the echo indication may be caused to move across the screen until the echo pulse is aligned with the step and the distance to the object may then be read upon the revolution counter, or distance indicator I58, which is calibrated in units of distance.

The circuit arrangement shown in Fig. 4 is a modification of a portion of the range unit which may be substituted for the portion of Fig. 3 below the line X-X. The circuit arrangement is like that shown in Fig. 3 (the corresponding parts bein lsimilarly designated) except that the portion of the circuit of Fig. 3 including tube I02 for causing a sweep wave to be generated is omitted. the diode anodes III and H2 being c'onductively connected, and that the condenser CNS of 0.1 microfarad and 1,000 ohm resistor Rlilt of Fig. 4 are used instead of the circuit comprising elements RBI C5I C58, R83, C52 and R82 for connecting the anode of tube "M5 to the coaxial conductor cable H8. The modifiedcircuit of Fig. 4 therefore functions to generate a pedestal 9 upon which the selected timing impulse 25 is superposed, as shown at 2', Fig. 1A and for amplifying the selected impulse. The selected pulse or range pulse may be usedfor some purpose other than that of controlling the deflection of a cathode ray beam as shown in Fig. 3. For example, the range pulse from the coaxial conductor cable I I8 in Fig. 4 may be used together with an echo impulse to control a means for automatically causing the rotation of the shafts 29 and 35 of the variable condenser of the phase shifter 2| and of the variable resistor oi the RC delay circuit 29 in such manner that the range pulse is maintained in synchronisrn with an echo impulse. With such an arrangement the range can be read from the range indicator I50 without the need for manual rotation of the shafts by means of the handle I25.

The operation of the system may he better understood from a consideration oi: the curves of Fig. 7 which show the relationship between voltage and time at several parts of the RC relay circuit 23, in conjunction with the diagram of Fig. lA. Curve i29sho'ws the potential atthe cathodes of tubes I00 and 95. Curve I30 shows the potential at the cathode of tube 98 and at the grid of tube 98. Curve I3I shows the potential at the anode of tube 91 and at the cathode of tube 98. Curve I32 shows the potential at the cathode of tube 9!. Curve i33 shows the potential at the anode of tube I00. Curve I34 shows the potential at the anode of tube 98 which is impressed upon the pedestal and sweep wave generator.

At the time to, a starting impulse a produced by the starting pulse generator I5 initiates the square-topped Wave b produced by the start-stop circuit IE to start the timing wave 0 produced by the timing wave generator 20. The timing wave in turn causes the generation of the timing impulses e by the timing pulse generator 22. The cathode of tube 95 is maintained at a constant potential of 50 volts positive with respect to ground and the anode of tube I is maintained at a constant potential of 200 volts as indicated by curves I29 and I33, respectively. The initial voltage drop E0 across rheostat R52, and therefore the voltage across the capacity in shunt with R52, varies with the rheostat setting. The current through R52 is the anode current of tube which is limited to a safe operating value by the screen grid voltage. The initial potential at the anode of tube 95, the grid of tube 98, the cathode of tube 96 and at the grid of tube 98 is therefore at some value u greater than 50 volts and less than 200 volts depending upon the rheostat setting. When tube 95 is cut on? and the condenser C4I discharges, the potential rises from the value it toward the 200 volt asymptote as indicated by curve I30. With E0 variable the cathode potential of tube 98 must be made a function of the range setting. As indicated b curve I3I, this potential has an initial value below 200 volts and is obtained by means of the voltage divider R56, R51, condenser C46 and diode 9'I, 6 being equal to 2.718 which is approximately equal to the ratio of 35,000 ohms to 95,000 ohms, that is,

Condenser C45 is charged through diode 91 to the voltage across R51 and thepotential at the oathode of tube 98 is therefore 200 volts minusthe voltage to which C46 is charged.

The timing impulses from the timing pulse generator 22 are also impressed upon the cathode of tube 98 as shown by curve I3I. After a certain interval equal to the time constant of the condenser discharge circuit comprising rheostat R52 and condenser C4I, the grid potential of tube 98 will have increased sufiiciently that a negative impulse 33 will cause the tube 98 to become conducting with the result that the potential at the anode of tube 98 decreases sharply as indicated by curve I34.

The cathode potential of tube 91 also rises exponentially as indicated by the curve I32. When tube 98 becomes conducting, anode current from the 300 volt source flowing through tube 98 and resistor R59 charges condenser C46 to cause the cathode potential of tube 98 to rise as shown by the portion of curve I3I which is substantially parallel to the curve I30. At the time tmax the grid potential of tube 98 is decreased, due to the positive portion of the start-stop wave a being impressed upon the tube 95 and the flow of space ass sts current through tube 98 ceases. Shortly thereafter the potential or the cathode of diode 9'! is reduced below the potential of its anode and the diode passes space current until the anode and cathode of the diode 91 are at the same potential, The cathode of tube 98 is thus returned to its initial potential '0 and the circuit is ready to be started by a succeeding start-stop wave 1) at the time t'o.

The initial decrease in anode potential of tube 98 as indicated by curve I34 cuts off the triode 101165, Hit of the pedestal and sweep wave generator so that the pedestal wave g and the sweep wave h are initiated at the instant that the negative timing pulse 33 occurs so that the following positive timing pulse 26 will be superposed upon thepedestal for producing a range mark as indicated at i, Fig. 1A. Each complete revolution of the shaft 29 in one direction or the other shifts the phase of the timing wave in a corresponding direction through one cycle and each of the timing pulses is therefore shifted by an amount equal to the period of the timing wave. Revolving the shaft 29 also varies the setting of rheostat R52 to change the time constant of the condenser discharge circuit at such a rate that the interval between an impulse 33 of each series of impulses which causes the tube 98 to become conducting and the preceding starting impulse may be varied continuously in either direction over a range extendingfrom a value near zero to a maximum value. It is thus seen that the impulse 26 which follows the pulse 33 will be selected to produce a range mark at all times and that the time of occurrence of this range mark may be varied by the rotation of shaft 29, each revolution causing the mark to be produced earlier or later by an interval equal to the period or the timing pulse. Since the distance to the object, represented by the period of a single cycle of the timing wave, is the velocity of propagation of the radiated impulse divided by twice the frequency of the timing wave, it is seen that the indicator 32 may be calibrated in units of distance so that the range to the object may be read when the range impulse 26 occurs in synchronism with an echo pulse received from the object.

This application is a division of my application Serial No. 491,791, filed June 22, 1943, now U. S. Patent No. 2,422,204.

What is claimed is:

1. In combination, a time constant circuit having capacitance shunted by resistance, the time constant of said circuit being variable, a

space current device having an anode, a cathode and a control electrode, means for intermittently charging said capacitance to an initial voltage which may vary, said capacitance being discharged through said resistance during periods separating successive charging periods, a circuit connecting said control electrode and said cathode, and means for deriving from Said time constant circuit and impressing upon said grid-cathode circuit to control conduction of the path separating said anode and said cathode a voltage which decreases during each discharge period of said condenser at a rate to cause-said control electrode and cathode to reach substantially the same potential when said condenser has discharged for a period equal to the time constant of said time constant circuit irrespective of the initial voltage to which said condenser is charged.

'2. In combination, a time constant circuit having capacitance shunted by resistance, the

time constant of said circuit being variable, means for intermittently charging said capacitance to an initial voltage which may vary, said capacitance discharging through said resistance during periods separating succesive charging periods, means for deriving from said time constant circuit a first voltage corresponding to the voltage across said time constant circuit, means for setting up a second voltage substantially equal to said first voltage divided by a constant substantially equal to 2.7 and means for combining said voltages to set up a resultant voltage which reaches zero when said condenser has discharged from said initial voltage for a period equal to the time constant of said time constant circuit irrespective of the value of said initial voltage.

3. In combination, an electric discharge device a circuit connecting said anode and said cathode, a second circuit connecting said cathode and said control grid, means for impressing upon said control grid with respect to point of fixed potential in said grid-cathode circuit-a potential which rises exponentially with respect to time from an initial value of potential, means for impressing upon said cathode with respect to said fixed potential a potential the initial value of which is greater than the initial control grid potential, and means for superposing a series of alternate positive and negative timing impulses upon said cathode potential to cause current to flow in the anode-cathode circuit of said device due to the lowering of the cathode potential by one of said negative impulses which occurs when the grid potential has been increased sufiiciently with respect to the cathode potential.

4. A combination in accordance with claim 3 in which means are provided for varying the rate of increase of said exponentially rising control grid potential.

5. A combination in accordance with claim 3 in which means are provided for shifting the timing impulseswith respect to time continuously in either direction.

6. A combination in accordance with claim 3 in which are provided means for shifting the timing pulses with respect to time, and means for changing the time constant or the exponentially rising potential in direct proportion to the shift of the timing pulses.

7. In combination, an electric discharge device having a cathode, a control grid and an anode, means for impressing upon said control grid 3. potential which rises exponentially with respect to time from an initial value of potential, means for impressing upon said cathode a potential the initial value of which is greater than the initial control grid potential, means for superposing a series of alternate positive and negative timing impulses upon said cathode potential to cause current to flow in the anode-cathode circuit of said device due to the lowering of the cathode potential by one of said negative'impulses which r occurs when the grid potential has been increased sufiiciently with respect to the cathode potential, means for shifting the timing impulses with respect to time, means for changing the time constant of the exponentially rising control grid potential in direct proportion to the shift of the timing impulses, means responsive to a potential change produced at the anode of said electric discharge device when said anode current commences to flow for generating a pedestal impulse which has a duration less than the time interval between two successive positive timing impulses, and means responsive to said timing impulses and said pedestal impulse for causing the selection of the positive timing impulse immediately following the negative timing impulse which initiates the anode current flow, said positive timing impulse being superposed upon said pedestal impulse.

8. In combination, an electronic device comprising an anode, a cathode and a control electrode, a circuit connecting said control electrode and said cathode having a point of fixed potential therein, means for applying to said control electrode a potential which continuously increases with respect to said fixed potential'for a period of time, means for applying to said'cathode a potential which is positive with respect to that of said control electrode, means for applying to said anode a potential which is positive with respect to that of said cathode, a current path connecting said anode and cathode in which space current commences to flow when said control electrode potential has increased sufficiently with respect to said cathode potential, means in said current path for increasing said cathode potential in response to said space current comprising a, condenser the charge on which is varied due to said space current flowing therein and means for superposing upon said cathode potential recurring potential impulses one of which reduces the cathode potential suiiiciently with respect to the increasing control electrode potential to initiate the flow of space current.

LARNED A. MEACHAM.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS 

